Fan blade



y 1941- P. M. BRANNAN v 2,243,189

FAN BLADE Filed June 4, 1937 w '2 Sheets- Sheet 1 Arron Ex May 27, 1 9 1- P. M. BRANNAN FAN BLADE Filed June 4, 1937 2 Sheets-Sheet 2 a Z w M 0 M P arm 0.

Patented May 27, 1941 FAN BLADE Paul M. Brannan, St. Louis, Mo., assignor to The Emerson Electric Mfg. 00., St. Louis, Mo., a corporation of Missouri Application June 4, 1937, Serial No. 146,3:91

6 Claims.

The present invention relates generally to air circulators, and more particularly to a fan blade assembly and a fan blade.

An object of the present invention is to provide a fan blade which is constructed to throw or impel the majorvolume of air moved from the surface of the hubward two-thirds of the blade.

Another object is to provide a fan blade which, when in operation, will produce a minimum amount of noise.

Another object is to provide a fan blade, the leading edge of which is convex and the leading edge portion of which decreases-'inlpitch from theinner end to zero at a point substantially half the distance of the blade, after which the pitch is negative to the outer tip thereof.

Another object is to provide a fan blade, the air impelling surface of which is concave or dishshaped throughout its' major portion but which at its outer tip is substantially planar.

Another object is to provide a fan blade which is so constructed that, in comparison with a con ventional blade, the normal blade noise is materiallv decreased, yet in which the maximum air velocity is increased with resultant increase in depth off penetration without increasing the power input or changing the blade speed.

Another object is to provide a fan blade having a trafling portion. the point of maximum pitch of which is between. 35% and 45% outwardly from the axis of rotation along the radial length, said trailing portion decreasing in pitch both towards the axis ofrotation and towards the free end of the blade.

Another object is to provide a fan blade in which the axial blade displacement reaches a maximum at a point between and 67% of the radial length thereof.

Another object is to provide an improved air clrculator including a hemispherical blade supporting-cap and a plurality of air impelling blades.

Other. objects and advantages will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a side viewof an air circulator assembly constructed according to the present invention.

Fig. 2 is a front view of the air circulator assembly shown in Fig. 1.

Fig. 3 is an enlarged front view of one of the fan blades of the air circulator assembly shown in Fig. 1.

Fig. 4 is a section on the line a-b of Fig. 3;

Fig. 5 is a section on the line c-d of Fig. 3;

7 with the present invention. The airpirculfator l0 Fig. 6 is a section on the line c-fof Fig. 3; Fig. 7 is a section on the line g-h of Fig. 3; Fig. 8 is a section on the line i-j of Fig'. 3; Fig. 9 is a section on the line 10-1 of Fig. 3; Fig. 10 is a section on the line m--n of Fig. 3; Fig. 11 is a section on the line o-p of Fig. 3; Fig. 12 is a sectionon the line q-r of Fig. 3; Fig. 13 is a section on the line s-t of Fig. 3; Fig. 14 is a section on the line u-v of Fig. 3; and Fig; 15 is a section on the line w-a: of Fig. 3. Referring to the drawings more particularly by reference numerals, Ill indicates generally an air circulator assembly constructed in accordance includes a blade supporting cap and a plurality of blades l2. The cap II is substantially hemispherical in shape and has spaced apertures l3 through which a suitable tool is adapted to be inserted for the purpose of manipulating a set screw (not shown) forming a part of a supporting base (not shown) for the cap H. The blades l2 are fixed to the cap I I by rivets I4, or the like. Three blades l 2 are shown, but agreater or lesser number may be used.

In Fig. 3, there is shown on an enlarged scale one of the blades. I2.- Each blade l2 includes a convex leading edge l8 and a trailing edge is, the

latter of which comprises two spaced convex segments 20 and 2| and an intermediate connecting concave section 22. The leading edge It defines the free portion of the periphery of a leading portion l8, while the trailing edge l9 defines the free portion of the periphery of'a trailing portion IS. The inner and outer junctions of the leading edge I 8 and the trailing edge I I! are substantially at the points 23 and 24, respectively. A radius AA. which passes through the points 23 and 24, may be called the primary radius of the blade.

A series of section lines 0-42, 0-11, e -J, g-h, i-9, k-l. mn, 0-1), qr, st, 11-0, and w.1: mark oil? on the blade l2 in Fig. 3 the correspondingly indicated sections shown in Figs. 4-15. The surface contours of the blade l2 are thus shown by these sections. An inspection of the sections shows that the portion of greatest. pitch in the blade is the trailing edge portion substantially at .or slightly hubward of a point 25 on the trailing edge l9. From substantially the point 25 to- I wards the fixed end of the blade along the trailing edge IS the pitch of the trailing edge decreases slightly. From substantially the point 25 towards the free end of the blade l2 the pitch of the trailing edge decreases to such a degree that from a point 26 outwardly it is almost zero.

Further, the pitch of the edge I 9 decreases sufstantially 35% to 45% ,irom the inner end, said trailing portion denciently sharply irom thepoint 25 so that the axial blade displacement is a maximum substantially at the point 25 also. The axial blade displacement oi air is obtained here and conventionally-by the formula axial blade displacement will likewise be substantially zero in this area.

The major surface of the blade is concave or dish-shaped in configuration when viewed from its front face. The free end of the blade I2 from the section u--v outwardly is substantially planar.

The blade I! performs the major portion of its work in that two-thirds nearest the axis of rotation which is contrary to the usual Ian blade. The high'air velocities, with resultant eddy currents, are confined to an area near the hub, where the peripheral speed of the blade I! is relatively low. At and towards the tip of the blade I2, where the peripheral speed is high, the air velocities are too low to set up objectionable eddy currents. The construction reduces considerably the blade noise and increases the maximum air velocity with resultant increase in depth of penetration without increasing the power input or changing the speed. The use of negative pitch for the leading edge portion of the blade from the point 30 outwardly to the free tip assists to reduce noise. The maximum widthoi the blade is along'a line transverse to the blade hubward oi a line 50% of a radial blade length.

It is thus apparent that there has been provided an air circulator which is adapted to fultill all of the advantages and objects sought therefor. It is to be understood that the loregoing description and the accompanying drawings have been given by way of illustration and example, and not by way 01' limitation, the invention being limited only by the following claims.

What is claimed is: g a 1. A fan blade, said blade comprising a leading portion and a trailing portion, said trailing portion being of maximum pitch at a point subof a radial blade length creasing in pitch from said point of maximum pitch towards the outer end of the blade, said trailing portion being of substantially zero pitch at and towards the outer end, said leading portion being of negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to just short of the outward terminus of the leading edge.

2. A fan blade assemblage including a plurality of blades, each blade being so constructed that the maximum blade displacement is at a point hubward oi a point fifty percent. of a radial blade length of such nature that the maximum air velocity and the depth of penetration of the fan are increased without increase in normal blade speed and with decrease in blade noise, said blade including a trailing'portion which is of maximum pitch at a point substantially thirty-five percent. to forty-five percent. of a radial blade length from the inner end, said leading portion being 0! negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to outward terminus of the leading edge, said blade iurther including a tip portion 0! substantially zero pitch.

3. A ran blade including a leading edge. a leading portion, a trailing edge, and a trailing portion, said leading portion being of negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to just short of the outward terminus of the leading edge, said leading portion being or positive pitch from said point hubward, said trailing portion being of maximum pitch at a point thirty-five percent. to forty-five percent. of a radial blade length from the inner end.

4. A fan blade including a leading edge, ,a leading portion, a trailing edge, and a trailing portion, said leading portion being of negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to just short of the outward terminus of the leading edge, said trailing portion being of increasing pitch from the inward terminus of the trailing edge to an intermediate point substantially 35% to 45% of a radial blade length outwardly, said trailing portion being of decreasing pitch from said intermediate point on the trailing edge to substantially the outward terminus ot the leading edge.

5. A fan blade including a leading edge, a lead- I ing portion, a trailing edge, and a trailing portion, said leading portion being of negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to just short of the outward terminus of the leading edge, said leading portion being of positive pitch from said point hubward, said trailing portion being of maximum pitch at a point thirty-five percent. to forty-five percent, of a radial blade length from the inner end, said blade being of maximum width at a point hubward oil a point fifty-percent. of a radial blade length and of a construction to effect the maximum blade displacement of air at said area of maximum width.

6. A fan blade including a leading edge, a leading portion, a trailing edge, and a trailing portion, said leading portion being of negative pitch adjacent said leading edge from a point substantially mid-way between the termini of the leading edge to just short of the outward terminus of the leading edge, said trailing portion being of increasing pitch from the inward terminus of the trailing edge to an intermediate point substantially thirty-five percent. to forty-five percent. of a radial blade length outwardly, said just short 01'. the 

